Drill bit

ABSTRACT

A drill bit for drilling holes in metal sheets or panels in which the drill is of generally conical form having a series of cylindrical drill portions increasing progressively in diameter from the point end of the drill whereby a single drill may be employed to drill holes of various diameters within a given range. The drill has a single flute of generally right-angle form in cross section with the apex of the right angle extending generally along the axis of the bit. Each cylindrical portion has a beveled end connecting it with the next smaller cylindrical portion and this beveled end extends helically at a relatively small angle to provide the usual axial clearance and to limit the rate of feed of the drill into the work.

mit States Patent [191 @akes Sept. 11, 1973 DRILL BIT [76] Inventor:Harry C. Oakes, P.O. Box 331, Exammer Gll weldenfeld Wyoming, NY. 14591Attorney-Conrad ChrIstel et al.

[22] FIled: Dec. 30, 1971 ABSTRACT [21 1 Appl' 214054 A drill bit fordrilling holes in metal sheets or panels in which the drill is ofgenerally conical form having a se- [52] [1.8. CI. 408/224 ries ofcylindrical drill portions increasing progressively (51] Int. Cl B23b51/00 in diameter from the point end of the drill whereby a [58] Fieldof Search 408/224, 225, 223, single drill may be employed to drill holesof various di- 408/206 ameters within a given range. The drill has asingle flute of generally right-angle form in cross section with the[56] References Cited apex of the right angle extending generally alongthe UNITED STATES PATENTS axis of the bit. Each cylindrical portion hasa beveled end connecting it with the next smaller cylindrical portionand this beveled end extends helically at a rela- 3:564:945 2/1971 B dl408/224 tively small angle to provide the usual axial clearance dt 1''tth t ff d fth d'll't th k. FOREIGN PATENTS OR APPLICATIONS O e m e 0ee 0 e m o 6 725,505 5 1932 France 408/223 1 Claim, 2 Drawing Figures 17Z 7 25 )2 3 l4 l5 )6 I 4 w T L If I 30 PATENTED 1 i975 INVENTOR. HARRYC. OAKES Awh ATTORNEYS DRILL BIT BACKGROUND OF THE INVENTION Thisinvention relates to drill bits and particularly to drill bits fordrilling holes of various sizes in sheet metal or similar platesor'panels of moderate thickness.

In the prior art drill bits have been proposed which are generallyconical in shape and have a series of stepped cylindrical formationsgraduated as to size with multiple flutes therealong. By use of suchbits holes corresponding to the diameter of any of the steppedcylindrical surfaces may be formed by drilling into the work until thecylindrical formation of the desired diameter passes through the sheetor panel. Thus a hole is formed by successively drilling a series ofholes starting with the smallest diameter at the outer end of the drillbit and continuing until the desired diameter is reached.

Drills of this type are exemplified in Tisserant U.S. Pat. No.2,897,696, dated Aug. 4, 1959 and Bradley U.S. Pat. No. 3,564,945, datedFeb. 23, 1971. The drill bits of these patents have multiple fluteswhich interrupt the cylindrical portions of the stepped drill to aconsiderable extent, whereby concentricity of the drill is difficult tomaintain and particularly in drilling metal sheets inaccurate drillingresults.

SUMMARY OF THE INVENTION The present invention provides a stepped drillof this general type with a single longitudinal extending flute whichprovides a single cutting edge for each stepped cylindrical formation ofthe drill bit. By reason of this design a major portion of eachcylindrical formation is continuous and uninterrupted and thus givesmaximum bearing surface for each cylindrical formation in the drill holeas such hole is being formed and also during the beginning entry of thenext cylindrical formation into the work.

The drill bit of the present invention is further characterized by theprovision of a very much limited axial clearance which in turn limitsthe degree of axial feed of the drill in a given hole since the rate offeed with respect to the rotary speed ofthe drill cannot extend thehelix formed by the axial clearance of the frustoconical leading end ofeach cylindrical portion of the drill. This is particularly important inhand drilling where the rate of feed is difficult to control and is alsoespecially important in drilling relatively thin metal sheets wheredrills are prone to chew into and distort the metal instead of properlyremoving the same by cutting action of the drill bit. 1

BRIEF DESCRIPTION OF THE DRAWING DESCRIPTION OF THE ILLUSTRATEDEMBODIMENT In the drill bit illustrated in the drawing and described indetail herein'by way of example a drill body which is generally conicalis designated generally by the reference numeral 10 and has a shank IIat an end thereof for attachment to a conventional drill chuck. Theopposite end of the bit has a generally cylindrical drill portion 12 ofsmallest diameter, in the present instance one eighth inch.

Extending from portion 12 is a series of drill portions of successivelylarger diameters designated by the numerals 13 through 24. In thepresent instance these drill portions increase in diameter by incrementsof 1/32 of an inch to a maximum of one-half inch. A connectingcylindrical portion 25 is provided between the largest diameter drillportion 24 and shank 11.

A single flute 27 extends along the drill bit parallel to the axisthereof to provide a face 28 which intersects the peripheries of theseveral drill portions to provide cutting edges. The small end portion12 is provided with the usual drill point formation 30 and the severalportions 13 through 24 each connect with the adjacent smaller diameterportion by way of a similar angular or beveled formation.

It will be noted that the single flute 27 interrupts the periphery ofeach cylindrical portion by an angle of ninety degrees so that each suchportion has 270 degrees of uninterrupted periphery to maintainaccurately concentric bearing of all portions of the drill in the workas formation of the hole proceeds.

It will further be noted that the beveled leading end of eachcylindrical drill portion is provided with axial clearance so that suchbeveled leading end extends helically. In the present instance thisaxial clearance is at an angle of about 3 degrees, or at any ratebetween 2 and 5 degrees. In a drill of the present type which isemployed in large part for drilling sheet metal and is usually hand-heldand hand-fed this sharply limited axial clearance serves to preventfeeding of the drill at too rapid a rate for clean drilling and alsoserves to prevent the drill from tearing into the work, as often occursin drilling relatively thin metal sheets.

A preferred embodiment has been described herein and shown in theaccompanying drawings to illustrate the underlying principles of theinvention but it is to be understood that numerous modifications may bemade without departing from the broad spirit and scope of the invention.

I claim:

l. A drill bit for drilling holes of various selected diameters in metalsheets comprising a tapered drill body comprising a series ofcylindrical portions increasing progressively in diameter from the smallend of said body, beveled shoulders connecting the several cylindricalportions, a single flute extending along said drill body and havingdefining wall portions extending parallel to the axis of said drillbody, said beveled shoulders extending helically at an angle of betweentwo and five degrees to provide axial clearance and limit the rate offeed of said bit into the work, and said flute defining approximately aright angle with its apex generally coincident with the axis of saiddrill body, whereby approximately three-fourths of the periphery of eachcylindrical portion is in continuous contact with the work.

ll i i

1. A drill bit for drilling holes of various selected diameters in metalsheets comprising a tapered drill body comprising a series ofcylindrical portions increasing progressively in diameter from the smallend of said body, beveled shoulders connecting the several cylindricalportions, a single flute extending along said drill body and havingdefining wall portions extending parallel to the axis of said drillbody, said beveled shoulders extending helically at an angle of betweentwo and five degrees to provide axial clearance and limit the rate offeed of said bit into the work, and said flute defining approximately aright angle with its apex generally coincident with the axis of saiddrill body, whereby approximately three-fourths of the periphery of eachcylindrical portion is in continuous contact with the work.